It is a fairly recent phenomenon that public health officials have become alarmed at the affect of Radon on the health of the public and, particularly, on its having a role in causing lung cancer. Radon is a radioactive gas that originates naturally in the earth and is a decay product of the radioactive isotopes of polonium, lead, and bismuth. When this gas emerges into the open air, its concentration is reduced to a great extent and there is little danger of ill effects of it. Starting in about the year 1970, however, home owners became very concerned with airflow and heat transfer through the walls of their homes. Both factors cause a loss of heat and, therefore, procedures were taken to insulate the walls of homes and to seal any possible crack that would allow the loss of heated air. This has caused a reduction (at least throughout the United States) in the rate of air exchange between the inside and the outside residences, so that, when radon enters the living space, it stays there for a longer period of time. In the United States the amount of radon which investigators have found in homes varies to a great extent by at least four orders of magnitude. In terms of the normal measurement of radiation called "becquerels" per cubic meter of air, the enclosure concentration can vary from a few "becquerels" per cubic meter of air, to more than 10 thousand; the average level is about 50 "becquerels". This average indoor level represents a radiation dose of about 3 times larger than the dose a person obtains from X-rays and other medical procedures in the course of his lifetime. It has been stated that hundreds of thousands of Americans living in high radon houses receive more radiation than people living in the vicinity of the Chernobyl Nuclear Power Plant, when one of its reactors exploded. In any case, the concern with the radon problem has caused many investigators to work on ways of limiting the amount of radon in residences.
One method, for instance, of reducing radon is to form a large cavity under the foundation slab of the house and to have a small fan pumping the resulting gas into the open air. This reduces the pressure of radon on the foundation and, therefore, limits the flow of the gas from below the cellar floor into the living area. Another method, of course, is to increase the ventilation in the house by a fan which removes air from the house and introduces cleaner outside air; that is to say, one can change the air in the house more frequently. This has the disadvantage of increasing ones fuel cost. The fan pumping radon from under the foundation involves a piece of mechanical equipment which can become out-of-order and which must be maintained. Furthermore, any cavity under the building presents structural problems, as well as eventually becoming filled with dirt or water. The method of reducing radon that is highly recommended is to fill any cracks or holes in the foundation with a sealing compound. The difficulty with this procedure is that concrete and other foundation materials are not impervious to gas, so that the radon is able to permeate and pass through the foundation, even when all the cracks and the holes have been sealed. These and other difficulties experienced with the prior art methods have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a system for shielding a building foundation against the passage of radon, which system can be used when the foundation is first made or can be applied to a building whose foundation has existed for sometime.
Another object of this invention is the provision of a shield for a building foundation, which shield can be applied as the foundation is being formed.
A further object of the present invention is the provision of a shield for excluding radon from a building having a pre-existing foundation.
It is another object of the instant invention to provide a shield for a building foundation, which shield is simple in construction, which can be readily applied making use of inexpensive materials, and which is capable of a long life of useful service with a minimum of maintenance.
A still further object of the invention is the provision of a shield for radon which will maintain its integrity for a long period of time without attention.
It is a further object of the invention to provide a foundation shield which not only will exclude gases such as radioactive radon, but also will exclude moisture and other chemicals.